1. Field of Invention
This invention relates to a halogen-free resin composition containing metal hydroxide, to a method of making the composition and to electrical wire having this resin composition as a covering on an electrical conductor core. Such an electrical wire is useful, for example, in a motor vehicle.
2. Description of Related Art
Polyvinyl chloride has been widely used as the covering material of electrical wire for an automobile, because it is superior in properties such as mechanical strength, extrusion processability, flexibility and coloring property. However, with recent concern for the global environment, halogen-free resin material has come to be used for the production of automobile parts including the covering of electrical wires in an automobile in place of polyvinyl chloride, because polyvinyl chloride discharges a harmful halogen gas on combustion.
A halogen-free resin composition in which a metal hydroxide is blended with a polyolefin-base polymer as a flame-retardant is known as a wear resistant resin composition having the merit of no generation of a poisonous gas such as a halogen gas on combustion (see JP-A-7-176219, JP-A-7-78518 and the like). In order that such a flame-retarding resin composition has a self-extinction property, a large quantity of a metal hydroxide is required to be added; however, this causes problems that mechanical strength such as the:wear resistance, tensile strength and the like of the composition are much reduced. In order to prevent the deterioration of mechanical strength, it may be considered that amounts of a polypropylene having a comparatively high hardness and a high density polyethylene are increased, but the flexibility of the covered electrical wire is reduced thereby and the processability becomes poor.
Various specific prior art proposals in this field will now be mentioned.
JP-A-6-290638 discloses resin compositions containing metal hydroxide for electrical wire insulation, in which the resin composition is based on polypropylene ( greater than 80%). Additional components are polyethylene modified with acid anhydride and styrene copolymer.
U.S. Pat. No. 5,561,185 describes resin composition for electrical wires containing metal hydroxide, in which the resin components are (a) 40-88.5% by weight of propylene which is 50% by weight or more of a ethylene/propylene random copolymer, (b) 1.5 to 30% by weight of a polyethylene modified with carboxylic acid derivative, e.g. maleic anhydride and (c) 10 to 48% by weight of an ethylene-series copolymer, typically ethylene/vinyl acetate copolymer.
U.S. Pat. No. 5,180,889 also describes a resin composition containing metal hydroxide as a covering of conductors in a crush resistant cable assembly. The resin components are (a) a low density copolymer of ethylene and alpha-olefin, (b) an elastomeric styrene-ethylene-butylene-styrene tri-block copolymer, preferably modified with maleic anhydride and (c) optionally an impact propylene and copolymer or polypropylene. Component (a) in the examples is 50% by weight or more of the total resin components.
An object of the present invention is to provide a halogen-free olefin-based resin composition comprising a mixture of components providing a good balance of properties, for example wear resistance, flame resistance, tensile property, flexibility and the like which are required for the covering material of an electrical wire, e.g. for an automobile.
The present invention provides a resin composition containing the following resin components:
(a) 30-80 parts by weight of a polyolefin thermoplastic elastomer having a melting point of 130xc2x0 C. or more and a Shore hardness of 90 or less,
(b) 1-20 parts by weight of a polypropylene modified with 0.1-10% by weight of an acid anhydride,
(c) 5-50 parts by weight of a styrene-based polymeric elastomer, and
(d) 10-30 parts by weight of a propylene polymer having a melt flow rate of 0.1 to 5 g/10 min and selected from propylene homopolymers and propylene-ethylene copolymers having a propylene content of at least 50% by weight,
wherein the total amount of the components (a), (b), (c) and (d) is 100 parts by weight and substantially no other resin component is present in the composition,
and further containing
(e) 30-200 parts by weight of a metal hydroxide, based on 100 parts by weight of the resin components.
The invention also provides an electrical wire having this composition as a covering or a conductor.
The respective components contained in the composition of the: present invention are carefully selected to provide the desired properties and are illustrated as follows.
The polyolefin thermoplastic elastomer (a) is preferably based on propylene and ethylene. A block copolymer of polypropylene with a propylene-ethylene rubber (for example, PER T310 and the like, which are commercially available from Tokuyama Co., Ltd.) is preferable. This type of polymer has hard segments of polypropylene and soft segments of ethylene-propylene copolymer in the molecule. The hard segment content is preferably 5-50% by weight, more preferably 15-45% by weight. An alternative preference for component (a) is an elastomeric propylene-ethylene random or block copolymer. When the melting point is less than 130xc2x0 C., the heat resistance of the whole composition is inferior, and when the Shore A hardness exceeds 90, the whole composition is too hard.
The amount of component (a) is 30-80 parts by weight relative to the total polymer amount (a), (b), (c) and (d), and preferably is in the range 40-60 parts by weight. When the proportion of the polyolefin thermoplastic elastomer (a) exceeds 80 parts by weight, the wear resistance of the composition is lowered. On the other hand, when this proportion is less than 30 parts by weight, the composition becomes hard and the processability is reduced.
The component (b) is a polypropylene modified with 0.1-10% by weight of a carboxylic acid anhydride typically an unsaturated acid anhydride, for example maleic anhydride.
The amount of component (b), per 100 parts by weight of total polymer (a), (b), (c) and (d), is 1-20 parts by weight, preferably 5-20 parts by weight. When the proportion of component (b) exceeds this upper limit, it reacts intensively with the metal hydroxide, so that the tensile elongation of the composition is lowered and the flexibility of the composition is reduced. On the other hand, when its proportion is less than 1 part by weight the wear resistance of the resin composition is not improved.
The polypropylene component (b) gives the composition heat resistance, both during extrusion and if over-heating occurs in use, e.g. in an automobile.
The styrene-based polymeric elastomer, component (c), is an elastomer polymer containing styrene monomer units. Preferably the styrene-based polymer has the structure of a block copolymer of styrene monomers and olefin monomers. This polymeric elastomer may be modified with 0.1-10% by weight of carboxylic acid anhydride, typically unsaturated acid anhydride, e.g. maleic anhydride. A preferred example of the styrene-based elastomer (not modified with acid anhydride or so modified) is a polymer obtained by block-copolymerizing styrene with butadiene, and saturating double bonds of the resulting block-copolymer by hydrogenation (known as SEBS). Typically the ratio of the styrene/butadiene is in the range 3/7 to 2/8 by weight. Alternatively there is used, for example, a styrene-based elastomer obtained by block polymerizing styrene and isoprene and hydrogenating the double bonds of the block copolymer (this product can be regarded as polystyrene-poly(ethylene-propylene)-polystyrene, and is known as SEPS).
The amount of component (c) per 100 parts by weight of total polymer (a), (b), (c) and (d) in the composition is 5-50 parts by weight, preferably 10-30 parts by weight. When the proportion of component (c) exceeds 50 parts by weight, the wear resistance of the composition is not improved. On the other hand, when its proportion is less than 5 parts by weight, the flexibility of the composition is inferior.
As the propylene polymer, component (d), propylene-based polymers are used, for example a propylene homopolymer or a propylene-ethylene copolymer of block or random type whose main monomer component (more than 50% by weight) is propylene. The propylene polymer (d) has a melt flow rate (MFR) of 0.1-5 g/10 min. MFR is measured in accordance with JIS K6921-2, the entire disclosure of which is incorporated herein by reference. Examples of the propylene polymer of MFR 0.1 to 5 g/10 min are RB610A, RB410, RB110 and the like, which are commercially available from Tokuyama Co., Ltd. MFR is indicative of molecular length. The preferred range of 0.1-5 g/10 min achieves good cold weather performance, particularly avoidance of cracking. As described in JIS K6921-2, melt flow rate is measured using a load of 2.16 kgf at 230xc2x0 C.
The amount of component (d), per 100 parts by weight of total polymer (a), (b), (c) and (d), in the composition is 10-30 parts by weight, preferably 20-30 parts by weight. When the amount of component (d) exceeds 30 parts by weight, the flexibility of the composition is poor and processing becomes difficult. On the other hand, when the proportion of component (d) is less than 10 parts by weight, the wear resistance of the composition may be reduced.
Magnesium hydroxide, aluminum hydroxide and the like can be used as the metal hydroxide (e). It is preferable that the particles of metal hydroxide are surface-treated with a coupling agent, particularly a silane coupling agent (for example, an aminosilane coupling agent, a vinylsilane coupling agent, an epoxysilane coupling agent, etc.) and optionally a surface-treating agent such as a higher aliphatic acid (for example, stearic acid, oleic acid, etc.) or the like. The silane coupling agent typically contains Sixe2x80x94O linkages which bond to the hydroxide. Magnesium hydroxide or aluminum hydroxide surface-treated with an amino-silane coupling agent is preferred in particular.
The amount of the metal hydroxide per 100 parts by weight of total polymer (a), (b), (c) and (d) in the composition is in the range 30-200 parts by weight, preferably 50-150 parts by weight and more preferably 70-100 parts by weight. When the amount of the metal hydroxide is too large, the elongation of the composition is deteriorated and the wear resistance, flexibility and processability are poor. On the other hand, when the amount of the metal hydroxide is too small, the flame resistance of the composition is reduced.
Optionally, there may be included a silicone oil, which typically is a high molecular weight silicone polymer but is liquid at room temperature (20xc2x0 C.), and which may be added into the resin composition as a blend with a synthetic resin carrier (this resin carrier is in this case preferably an additional resin component, not comprised in the components (a), (b), (c) and (d)). The amount of resin carrier, if present, is selected to achieve the desired processability when handling the oil and incorporating it in the mixture, and may be in the range 30-70%, more preferably 40-60%, by weight of the blend of silicone oil and carrier resin.
The type of the resin used as the carrier resin is not specifically limited, but a polypropylene, a low density polyethylene, a linear low density polyethylene, a general purpose polystyrene (GPPS), a high impact polystyrene, a polyamide 6, a polyamide 66, a polyoxymethylene, an ABS resin, a polybutylene terephthalate, a polyethylene terephthalate, an ethylene-methyl methacrylate copolymer and the like are suitable examples. These can be used alone or as a mixture of two or more.
Such a silicone oil mixed with a resin is commercially available as xe2x80x9cSi concentratexe2x80x9d from Toray-Dow Corning Silicone Co., Ltd., with the following resin components and product numbers:
Polypropylene-base: BY27-001, BY27-201, BY27-201C.
Low density polyethylene-base: BY27-002.
Linear low density polyethylene-base: BY27-202.
General purpose polystyrene: BY27-003.
High impact polystyrene: BY27-004.
Polyamide 6-base: BY27-011.
Polyamide 66-base: BY27-005.
Polyoxymethylene-base: BY27-006.
ABS resin-base: BY29-007.
Polybutyrene terephthalate-base: BY27-009.
Polyethylene terephthalate-base: BY27-112.
Ethylene-methyl methacrylate copolymer-base: BY27-202M.
The amount of the silicone oil, based on the total amount of the components (a)-(e) is 0.5-5% by weight or less, preferably at least 1%.
When the amount of silicone oil is within the range 1-5%, the: conductor-drawing force (measured as described below) of the resin composition is acceptable and the flexibility is improved. Further, the surface-lubricity of the resin composition is improved and the wear resistance is remarkably improved.
All of the components (a), (b), (c) and (d) are selected to be halogen-free. Synthetic resin components other than (a), (b), (c) and (d) are substantially, and preferably completely, absent, except in the case where the carrier resin for the silicone oil is present, as described above. The components (a), (b), (c) and (d) are selected to be all different from each other.
Compounding agents usually included in an olefin-based resin composition, for example an oxidation inhibitor, a copper inhibitor, a lubricant and the like may be added in the resin composition of the present invention in amounts which do not unacceptably reduce the above-mentioned properties. These and other conventional additives will be readily apparent to those of ordinary skill in the
The resin composition of the present invention can be prepared by mixing and kneading the above-mentioned respective components by conventional methods.
The method of covering an electrical wire, particularly an electrical wire for a motor vehicle such as an automobile, by the resin composition of the present invention may similarly be performed by a conventional method.
The resin composition of the present invention when used as the covering material of an electrical wire, e.g. for an automobile, can well satisfy requirements for properties such as wear resistance, flame resistance, tensile property, flexibility, heat resistance, cold resistance and the like.
In particular, when as preferred the metal hydroxide particles are surface-treated with an amino-silane coupling agent, the coupling agent bonds the metal hydroxide with the acid anhydride. The coupling agent has a functional group reacting with the inorganic hydroxide and a functional group reacting with the organic acid anhydride. Also, the epoxysilane and vinylsilane coupling agents, if used, have affinity to the hydroxide and the anhydride. Accordingly, the wear resistance of the resin composition is remarkably improved. Further, when an amino group is present on the lipophilic side of the silane coupling agent molecule, the reaction with the polyolefin modified with an acid anhydride can advantageously suppress the hydrophilic property of the amino group.